1. Field of the Invention
The present invention relates to coated seeds and a process for preparing coated seeds.
2. Background of the Art
Seed coating is a practice which has become widespread. It is aimed in particular at improving the germination characteristics, at providing various additives capable of intervening at any time during the formation and growth of plants, at protecting the seeds or at imparting to the seed a shape or a size which is suitable for automatic sowing. It has thus been proposed to coat seeds by means of nutrients, fillers, fungicides, herbicides, insecticides, and the like.
However, the known coating processes have numerous disadvantages.
Frequently the coating does not adhere properly to the seed with the result that it does not withstand the various handling operations to which the seeds are subjected. This phenomenon is particularly sensitive in the case of the seeds with rapid water uptake. In fact, during the coating operation, considerable swelling is frequently observed in some seeds owing to water absorption. After drying, the seed retracts to regain its original size while the coating does not generally contract to the same extent; as a result, it no longer adheres properly to the seed and it becomes brittle, crumbles or disintegrates.
On the other hand, some coatings are so hard and tough that they do not dissolve or disintegrate readily under the effect of moisture and water once the seed has been sown, which is equally detrimental.
During the coating, use is made of small quantities of water, particularly for moistening the seeds before the coating operation as such, to solubilise or disperse at least one of the constituents of the coating or to solubilise or disperse the adhesive agents employed to ensure the adhesion of the other constituents of the coating. The presence of water presents disadvantages which are particularly marked when the seeds are poorly protected and absorb water rapidly. In fact, some seeds can absorb water during the coating operation, which may result in a premature initiation of germination, with the result that the seeds can no longer be stored. Furthermore, it is frequently impossible to dry the seed correctly under the coating layer, which entails risks of spoilage during the storage. These effects are particularly sensitive when the seeds employed are seeds of leguminous plants, maize and crucifers.
Moreover, some constituents of the coating, which on the whole have properties of interest, can have secondary effects of phytotoxicity for some seeds.
Finally, in some cases, it is difficult to coat the seeds in a uniform manner because their surfaces are not regular and do not permit a uniform attachment of the coatings. The adhesive agents which are usually employed to cause the other constituents of the coating to adhere to the seed do not allow all these disadvantages to be overcome simultaneously.